Color process



Nov. 7, 1933. J. A. LUCAS 1,934,367

COLOR PROCESS Filed Aug. 1, 1931 Fig.1

' Fig. 3

JOSEPH ALFRED LUCAS M W ?atented Nova 7, 1933 ilNiTED STATE Paras-tr eerie insist? This invention relates to the preparation oi process color plates or cuts.

In the process now in general use for the production of color plates or cuts a number of photo= graphic negatives of the object to be reproduced are made in a camera adapted to use panchromatic plates or films. The negatives are made through filters of different colors and a screen of predetermined mesh arranged at difierent 1o angles. The negatives so made are called separation negatives and from them cuts are produced which represent the tone values of the complementary colors of the filters used.

In the known method briefly described above it is necessary for, the engraver to consider color at every step of the process and as the work progresses it is not uncommon to accumulate errors in color.

In order to check and possibly correct color errors the engraver is required to make frequent test prints from the cuts and etch, re-etch or burnish, if necessary, one or more of them to get the proper tone values. Each time this work is done or repeated the process becomes more complicated and expensive and requires additional time.

It is the main object of the present invention to simplify the process of preparing cuts for color printing by shortening the number of steps so and the time required by the simultaneous formation of a plurality of screened cuts from a plurality of monotone positives representing the primary color values of the copy without the necessity of comparing the colors of the objectat any stage of the process.

The invention is disclosed diagrammatically in the accompanying drawing in which:-

Figure 1 represents a set of negatives of a golored object made through different color filers;

Fig. 2 represents a set of positives made from the negatives of Fig. 1;

Fig. 3 represents the same set of positives mounted in angular relation toa screen ready for 43 making hali-tonecuts, and

Fig. 4 represents a set of cuts produced from the arrangement of Fig. 3 reblocked and ready for printing with colored inks.

In the established color process three or more photographs or the colored object, or a colored representation of it, are taken through different color filters'and a screen set at different angles. These are known as separation negatives and from positives prepared from them cuts are made and the engraver then makes prints in colored inks, compares the resulting color combinations with the original and, when necessary to int-en sii'y or reduce one or more colors, burriishes or re-etches the cuts. In this process it is necessary to consider color at all times, whereas in accordance with the present invention the en= graver is furnished with positive nionotones made from separation negatives taken through color filters only on panchromatic films or plates. He then prepares cuts by the use of a single screen 85 common to all monotones. It is not necessary for him at any stage of the process to compare or even see the original colors.

In carrying the invention into practice, in the manner illustrated by the drawing, only three 7@ negatives, positives and cuts are shown. It is to be understood, however, that the number is so limited for convenience of illustration only and that in practice more than threecuts may be made if the result required demands very accurate color gradations.

Figure 1 represents a set of photographic nega= tives of the object to be reproduced in color made through different color filters without the use of any screen, the negatives being identical in every respect except that of color value. The numeral 1 represents a. photographic negative of the colored object made through an orange red color filter, 2 represents a negative made through a blue filter and 3 represents a negative made through a green filter. The negatives thus produced through the several color screens are ordinary photographic negatives in black, white and gradations of gray and difier from one another only in that their shading is different, being dependent upon the color values of the original object. This difference in shading or density is indicated in the drawing by a difference in the size of cross hatching used in the representation of the several negatives. The size of cross hatching is not intended 5 to indicate relative density oi the negatives but merely to indicate that the negatives diner from one another in density. The actual relative densities of the negatives would of course depend upon the color of the object photographed. I

From the separation negatives thus produced, photographic positives are made. Numeral d represents the photographic positive made from negative 1, which was taken through an orange red filter. This positive will represent the value oi the color complementary to that of the screen through which the original negative was made and will hence represent the blue color values oi the original object photographed.

Similarly a photographic positive 5 is made 119 Mill from the negative 2, which was taken through a blue filter. This positive will hence represent the color value of the yellow tints of the object.

A photographic positive 6 is likewise made from the negative 3 and will represent the red color values since a green filter was used in making the negative. These three positives are alike except that they differ from one another in density and shading dependent upon the color of the object photographed.

The next step in the process is indicated in Fig. 3-w.hich represents the three photographic positives of Fig. 2 mounted for reproduction through-a common screen 7. The positive5 is mounted with its base horizontal whereby the screen lines are at an angle of 45 with its base. Positives 4 and 6- are each mounted'at an angle, preferably 30. with the horizontal so that the screen lines are at angles of 15 and 75 respectively with-their bases, the two positives being inclined in opposite directions as illustrated in" the drawing.

From the positives .4, 5 and 6 arranged as shown in Fig. 3 a common negative is made through the screen '7 upon a single photographic plate and from this negative a single cut or plate is made upon a suitable surface. for example, a sensitized sheet of copper or zinc. After-this composite plate or cut has been properly developed and etched the individual cuts or plates 9, 10 and 11 from which the printing is to be done are severed therefrom .and mounted on suitable blocks 8 as shown in Fig. 4:

The intersecting lines in Fig. 4 represent the half tone effect produced by the screen '7. It is to be noted that the screen is not used until the step of making the second negatives, thereby eliminating the use of cumbersome equipment on the camera when taking the original negatives.. Furthermore, by using a common screen and by arranging the positives in angular relationship to one another as shown in Fig. 3 the correct relation between the screen lines and the severed positives to avoid moir effect in the finished reproduction is obtained without the necessity of adjusting screen angles for each exposure.

The screen '7 in Fig. 3 and the corresponding screen effect appearing on the cuts of Fig. 4 are diagrammatic only, no attempt having been made to show the actual mesh to scale. The lines merely represent a screen having two sets of equally spaced lines at right angles to one another and show the direction of the lines forming the screen. Screens in practice are made with meshes varying from 50 to 300 lines per inch, the selection of the proper screen depending upon the kind of printing required.

By making a common negative from the three separate positives and a common plate or cut from this single composite negative, uniformity and correct color balance of the finished print are assured. Where separate negatives and plates are made, there is always a possibility of variation between the several plates e. g. in sensitivity, exposure, developing and etching, whereby error in the finished print is introduced. These errors are eliminated by the present invention. Since the several intermediate negatives are made on a single photographic plate in one operation, and since the cuts are likewise made on a single plate of metal or other suitable material, there can be no variation in the factors which influence the production of the cuts and they will therefore represent the true color values of the original object. With this improved process, retouching of the cuts becomes unnecessary.

The actual process of printing in this invention is known, viz., the several cuts are inked with their respective colored inks and prints are made separately with the cuts in register superimposed one upon another and with a common base. Cuts made as disclosed in this invention. when used with their respective colored inks, will produce an almost perfect reproduction of the original colored object.

I claim:-

l. A method of preparing process color plates of cuts which comprises producing a plurality of filtered but unscreened separation negatives of an object to be reproduced, producing photographic positives therefrom, disposing said posi tives at different angles behind a common rectangularly-lined screen, making through said screen photographic negatives of said positives on a single plate in one operation, producing therefrom on suitable material a single composite cut and thereafter severing the said composite cut into individual cuts or color plates.

2. A method of preparing process color plates or cuts which comprises producing a plurality of filtered but unscreened photographic negatives, producing photographic positives therefrom, disposing the said positives in a'compact group be hind a common screen, making through said screen a single composite negative of the grouped positives, printing and etching a single composite cut from the last mentioned negative and thereafter severing the said composite cut into individual cuts or color plates.

3. A method of preparing a plurality of plates or cuts for color engraving which comprises producing on a single plate of suitable material a composite cut comprising all of the individual cuts for the different colors and thereafter severing the said composite cut into individual cuts or plates.

JOSEPH ALFRED LUCAS. 

